Mortise locks have experienced problems with the attachment of operating trim including knobs and levers to the locks. In a mortise lock installation, the mortise chassis is slid into an edge pocket in the door and it is secured and operated by a transverse square spindle inserted into the chassis. Operating members slide onto the spindle and are retained there by two flanges commonly called roses which are bolted together through the door. These roses carrying the knobs or levers. The knobs or levers must rotate freely independent of the rose, but they must be prevented from escaping axially from the rose.
In the past, the knobs or levers have been retained by snap rings, truarc rings, pins or set screws, none of which have proven to be entirely reliable, or adjustable for tolerance or wear.